From 6048eb34be4df5414641de439564608b23f83d93 Mon Sep 17 00:00:00 2001
From: Pascal Birchler <swissspidy@git.wordpress.org>
Date: Fri, 16 Jun 2023 12:56:03 +0000
Subject: [PATCH] I18N: Allow to short-circuit `load_textdomain()`.

Introduces a new `pre_load_textdomain` filter, which is useful for plugins to develop and test alternative loading/caching strategies for translations. This brings consistency with the existing `pre_load_script_translations` filter for JavaScript translations.

Props ocean90, swissspidy.
Fixes #58035.

git-svn-id: https://develop.svn.wordpress.org/trunk@55928 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-includes/l10n.php                    | 22 +++++++++++++++++++++
 tests/phpunit/tests/l10n/loadTextdomain.php | 16 +++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/src/wp-includes/l10n.php b/src/wp-includes/l10n.php
index a0c7bba903..9467a6b19c 100644
--- a/src/wp-includes/l10n.php
+++ b/src/wp-includes/l10n.php
@@ -717,6 +717,28 @@ function load_textdomain( $domain, $mofile, $locale = null ) {
 
 	$l10n_unloaded = (array) $l10n_unloaded;
 
+	/**
+	 * Filters whether to short-circuit loading .mo file.
+	 *
+	 * Returning a non-null value from the filter will effectively short-circuit
+	 * the loading, returning the passed value instead.
+	 *
+	 * @since 6.3.0
+	 *
+	 * @param bool|null   $loaded The result of loading a .mo file. Default null.
+	 * @param string      $domain Text domain. Unique identifier for retrieving translated strings.
+	 * @param string      $mofile Path to the MO file.
+	 * @param string|null $locale Locale.
+	 */
+	$loaded = apply_filters( 'pre_load_textdomain', null, $domain, $mofile, $locale );
+	if ( null !== $loaded ) {
+		if ( true === $loaded ) {
+			unset( $l10n_unloaded[ $domain ] );
+		}
+
+		return $loaded;
+	}
+
 	/**
 	 * Filters whether to override the .mo file loading.
 	 *
diff --git a/tests/phpunit/tests/l10n/loadTextdomain.php b/tests/phpunit/tests/l10n/loadTextdomain.php
index 26e567d663..234e98015a 100644
--- a/tests/phpunit/tests/l10n/loadTextdomain.php
+++ b/tests/phpunit/tests/l10n/loadTextdomain.php
@@ -300,4 +300,20 @@ class Tests_L10n_LoadTextdomain extends WP_UnitTestCase {
 
 		$this->assertSame( get_user_locale(), $this->locale );
 	}
+
+	/**
+	 * @ticket 58035
+	 *
+	 * @covers ::load_theme_textdomain
+	 */
+	public function test_pre_load_textdomain_filter() {
+		$override_load_textdomain_callback = new MockAction();
+		add_filter( 'override_load_textdomain', array( $override_load_textdomain_callback, 'action' ) );
+
+		add_filter( 'pre_load_textdomain', '__return_true' );
+		load_plugin_textdomain( 'wp-tests-domain' );
+		remove_filter( 'pre_load_textdomain', '__return_true' );
+
+		$this->assertSame( 0, $override_load_textdomain_callback->get_call_count(), 'Expected override_load_textdomain not to be called.' );
+	}
 }